NASA’s Swift observatory is designed to detect high-energy radiation coming from the most powerful explosions in the Universe: gamma-ray bursts.

But it’s also equipped with a more normal telescope, one that has a 30 centimeter mirror — that’s smaller than the one I have in my garage! But, this telescope is in space, so the atmosphere doesn’t blur out the images. More importantly, the air above our heads absorbs ultraviolet light, preventing ground-based telescopes from even seeing any UV light.

So Swift’s UVOT (Ultraviolet/Optical Telescope) may not be big, but it can easily see UV coming from astronomical objects. And it has a wide field of view, allowing it to get fantastic images of bigger things… like galaxies.

That’s M33 (click to embiggen), a very nearby galaxy; it’s part of our neighborhood of galaxies called the Local Group. It’s a hair under 3 million light years away, and it’s smaller than the Milky Way, about half our size and a tenth our mass. It’s actually visible with binoculars as a fuzzy patch not too far from its big brother, the Andromeda galaxy.

The funny thing is, we know that UV light is predominantly given off by star-forming regions in galaxies; gas clouds where stars are actively being born. The amount of UV from M33 indicates that it is ablaze with stars, cranking them out at a rate far higher than the Milky Way. So even though it’s a bit on the smallish side, it’s certainly pulling its weight when it comes to making stars.

This image is pretty cool. It’s a mosaic of 39 individual images totaling 11 hours of exposure time, using three different UV filters, and it’s the most detailed UV image of an entire galaxy ever taken. Not bad for a telescope built to do an entirely different kind of science!

I worked on the education and public outreach for Swift for several years, and I remember first reading about the UVOT and thinking, wow that’s a pretty small telescope. I wonder what it will be able to do? Then after a moment or two of some mental math I began to realize that this was in fact a fairly powerful telescope; it’s no Hubble, but it can do some terrific science. And it can also make some very pretty pictures.

I’m a Noobie so go easy on me, whats that odd spot to the right and a little below the centerline? It’s looks to me like maybe an issue with the telescope or the camera or but I’m curious in case it really is some sort of giant star with a glowing aura around it and some sort of stripe coming from it. I guess it could also be a much closer star but it looks like something that was added, at least to my untrained eye. Again I have no astronomy background, just a curious person. Thanks!

As the BA said, this image is a composite of a bunch of smaller images. The ‘streaks’ are simply some of the seams where the smaller images are joined together. If you look closely enough, you’ll find other similar, but smaller, streaks in the photo.

Swift uses CCDs, detectors pretty much like what’s in a your digital camera, but a lot more expensive. But they all suffer from what’s called blooming: when an object is too bright, the electrons in the detector can bleed down a column of pixels. You see it all the time in Hubble images, for example.

In this case, it looks to me like the star was too bright and bled. The image itself was probably rotated before publishing, which is why the line isn’t vertical.

As for the halo, I am not sure exactly why that’s there, but in CCDs it’s usually a problem with light being absorbed and basically scattered inside the detector. In the camera I used to use (STIS), the CCD was translucent to near infrared light, so the red light would get smeared a little bit around a bright red source. I had a project looking for low mass red dwarfs, so that made them easy to spot: just look for stars with halos!

I think that streak could be what’s called a “diffraction spike.” This happens in a reflector due to the spider-vanes that hold the secondary mirror standing in the path of the light from the source to the primary mirror. If the ‘scope’s a refractor, which I think the Swift is not, then you can artificially create one. (Amateur astrophotographers use strings in front of the primary lens, or create them using photoshop.)

Let’s see…a CM is 100 times larger than a MM, right? My refractor is 127mm which works out to about 5 inches, 300mm would then be about 12 inches in aperture, right? What kind of optics does this scope have and what is its focal length? This also says alot about what a telescope can do as you know better than I, Phil. I’m just curious here. I didn’t know that SWIFT had a scope like that on board. This is really cool, thanks for the post.

DenverAstro, 1cm = 10mm (centi = 1/100, milli=1/1000).
Also units cannot be freely capitalized or decapitalized(?!?); 1mm is
1 millimeter, but 1Mm is 1 megameter (mega = 1,000,000 = million)
– that’s a difference of a factor of 10^9 (billion in US lingo).
In the end you do work out the numbers correctly, though,
with 30cm=300mm. That’s a pretty large refractor you have there,
by the way – 127mm… Should be pretty good for M33.
Cheers, Regner Trampedach

Thanks for the explanation’s,
Just to be sure I’m understanding correctly. The haloed spot really is a very bright star, but it looks bigger and brighter than it should because it screws up the camera? Basically. And the streak through it is just a seam from putting the composite pictures together? I would have thought they would be at right angles to the picture, of course maybe they were before the picture was rotated and cropped.
Thanks again everyone, I’m really enjoying this site. Just makes me wish it wasn’t cold and cloudy at night.

The Ultraviolet/Optical Telescope on Swift (affectionately called UVOT) is a modified Ritchey-Chrétien telescope with a 30 cm primary mirror, a focal ratio of f/12.7, a field of view of 17′ x 17′ and a pixel scale of 0.5″/pixel. It can observe from about 1600 Angstrom to about 6000 Angstrom. It is one of three ultraviolet telescopes in orbit. There are more details at .